1. Field of the Invention
The present invention relates to a microwave power sensor and a method for manufacturing the same, and more particularly, to a microwave power sensor and a method for manufacturing the same, in which a heating resistor is connected with an input end and thermocouples are formed to be bilaterally symmetrical with respect to the heating resistor, so that it is easy to match impedance, an amount of reflection loss due to any parasitic components is small, and a linear output voltage proportional to an input electric power is obtained; and ground plates capable of radiating heat are further formed to be spaced apart from and around the heating resistor, so that the sensitivity of the sensor can be enhanced thanks to its high thermal impedance.
2. Description of the Prior Art
Generally, wireless communications can be made through smooth transmission of signals between transmitting and receiving ends.
At this time, if an RF (radio frequency) signal having insufficient electric power is transmitted from the transmitting end to the receiving end, the RF signal received by the receiving end cannot generate a desired output level.
For example, if a broadcast signal transmitted from a broadcasting station has insufficient electric power, a broadcasting image is distorted or a noisy voice is outputted in a television set, which is operated by the received broadcast signal.
Accordingly, in the wireless communications such as mobile communications and TV broadcasting, accurate measurement of signal electric power is the most basic and essential factor in transmitting and receiving information.
Recently, as there is a tendency for RF parts to be integrated, development of electric power sensors compatible with MMIC (monolithic microwave IC) or CMOS RF-IC has been attempted. Typically, NIST (U.S. National Institute of Standards and Technology) published a sensor employing thin films obtained through a CMOS standard process and diaphragms obtained through XeF2 dry etching.
However, the sensor can be used only in relatively low input power in view of characteristics thereof. Since the sensor is connected to a heating resistor having a relatively larger size compared to the wavelength of the microwave input, perpendicularly to a proceeding direction thereof, it is difficult to match impedance in broadband.
Moreover, since a ground electrode serving as a heat radiation plate is in the vicinity of the heating resistor, heat loss is increased.
In addition, since thermocouple temperature sensors cannot be disposed only at one side of the heating resistor, the conversion efficiency of the sensor is inevitably lowered.
Further, since a silicon surface, which has been removed by the dry etching, corresponding to a lower portion of the sensor is difficult to be flat, there are disadvantages in that impedance of a transmission line is not constant, and high manufacturing costs are expended.
Accordingly, the present invention is contemplated to solve the above problems in the prior art. An object of the present invention is to provide to a microwave power sensor and a method for manufacturing the same, in which a heating resistor is connected with an input end and thermocouples are formed to be bilaterally symmetrical with respect to the heating resistor, so that it is easy to match impedance, an amount of reflection loss due to any parasitic components is small, and a linear output voltage proportional to an input electric power is obtained; and ground plates capable of radiating heat are further formed to be spaced apart from and around the beating resistor, so that the sensitivity of the sensor can be enhanced thanks to its high thermal impedance.
According to an aspect of the present invention for accomplishing the objects, there is provided a microwave power sensor comprising a semiconductor substrate with a nitride or oxide film formed thereon; a membrane which is a portion of the nitride or oxide film is floated by removing a portion of the semiconductor substrate; first and second thermocouple groups are formed to be symmetrically spaced apart from each other on the membrane; an RF input end is formed on the nitride or oxide film; a heating resistor is formed on the membrane to be connected with the RF input end; first and second ground plates are formed on the nitride or oxide film at both sides of the RF input end; a third ground plate is formed on the nitride or oxide film to be connected with the heating resistor and electrically connected with the first and second ground plates; and first and second output terminals are formed on the semiconductor substrate to be connected with the first and second thermocouple groups, respectively.
According to an aspect of the present invention for accomplishing the objects, there is provided a method for manufacturing a microwave power sensor comprising a first step of forming top and bottom silicon nitride films on top and bottom surfaces of a silicon substrate, respectively, and etching an inner side of the bottom silicon nitride film to expose the bottom surface of the silicon substrate; a second step of forming one kind of polysilicon patterns for thermocouples and a polysilicon pattern for a heating resistor on the top silicon nitride film; a third step of depositing a metal on the top silicon nitride film to form the other kind of metal patterns for the thermocouples, and metal patterns for an RF input end, ground plates and output terminals; a fourth step of exposing the metal patterns corresponding to the ground plates and forming a sacrificial layer on the whole surface; a fifth step of removing the sacrificial layer to expose the metal patterns corresponding to the ground plates; a sixth step of depositing a seed layer for electroplating on the whole surface of the sacrificial layer and the exposed metal patterns; a seventh step of forming a electroplating wall on the seed layer, an eighth step of electroplating a metal inside of the electroplating wall to form a ground electrode for electrically connecting the metal patterns corresponding to the ground plates; a ninth step of removing the sacrificial layer and the electroplating wall so that the ground electrode is floated from the substrate; and a tenth step of removing the bottom surface of the exposed silicon substrate so that the polysilicon pattern for the heating resistor and a portion of the silicon nitride film around the polysilicon pattern are floated.